Method for the manufacture of concrete structures



P 1962 B. c; GERWXCK 3,055,077

METHOD FOR THE MANUFACTURE OF CONCRETE STRUCTURES Filed April 10, 1958 pRgsb Rg SOURCE INVENTOR. BEN C. GERW/CK ATTORNEYS Unite This invention relates to methods for the manufacture of concrete structures.

In the forming of many prestressed or precast concrete objects, such as I and T girders and beams, octagonal concrete piling and the like, it is necessary to use mold forms having downwardly directed return surfaces. One difficulty with forms of this type is a tendency for pockets of water and air to collect adjacent the return surfaces during the curing of the concrete material. Apparently the water, being less dense than the other materials in the concrete mix, tends to rise much as the air bubbles rise until it is trapped within the concrete mix at the mold surface. Adjacent upper exposed openings of the mold, these water pockets create no problem since the mix can be agitated and smoothed by hand to provide an unmarked outer surface. However, in the areas adjacent the return surfaces of the mold, evaporation and escape of the water leave unsightly pock marks on the outer surfaces of the concrete. A further problem is that these deformities are only discovered when the mold form is removed' In prestressed concrete structures, these pock marks also are particularly objectionable in that they detract from a desired thickness of concrete over the reinforcing steel and prestressing strands extending through the concrete. Accordingly, grout filling of the pock marks and depressions is not a satisfactory solution to the problem.

In general, it is an object of the present invention to provide improved methods of forming prestressed or precast concrete objects by which pock marks and holes due to the collection of water and air adjacent return surfaces of a mold are virtually eliminated.

Another object of the invention is to provide means for carrying out the improved method of the character described which is inexpensive and easily adapted to existing manufacturing procedures.

Other objects and advantages of the invention will appear from the following description and from the draw ings in which:

FIGURE 1 is a view in perspective of means useful in carrying out the invention;

FIGURE 2 is a diagrammatic representation of the use of the device shown in FIGURE 1, for example, in conjunction with the manufacture of octagonal piling;

FIGURE 3 is a view in section and elevation along the line 33 of FIGURE 2;

FIGURE 4 is a detail view in section along the line -4-4 of FIGURE 3; and

FIGURES 5A, B and C are a diagrammatic representation in sequence, illustrating the method of the invention.

Generally stated, the present invention is based on the discovery that if partially cured concrete adjacent return surfaces of a mold form is subjected to an upwardly rising stream of fluid, such as water or air under pressure, such stream of fluid will tend to channel undesired existing pockets of air and water to an upper exposed surface of the form where they can be eliminated. The most satisfactory results are obtained if the concrete is allowed to remain in a quiescent state after the initial pouring, or until it has achieved a stiff, partially cured state. It has been found that in such state the channelling effect produced by the upwardly rising streams of fluid is enhanced.

without permanent deformation of the concrete mix.

States Patent I partially set.

Referring to the drawings, FIGURE 1 illustrate one form of a device for injecting streams of fluid beneath the surface of partially cured concrete. As shown, the device comprises a paddle-like member 10 including a rigid substantially flat frame 12 and a handle 14. Extending lengthwise of the frame and integral therewith are a plurality of fluid conduit means 16, each provided with one or more apertures 18 for the escape or projection of tiny streams of air or water in a direction away from the base of the frame 12. A main supply conduit 20 communicates with the opposite ends of the conduits 16, and is supplied with fluid from a pressure source 22 through a suitable valve 24. The source 22 may be either water, as from a conventional water main, or a supply of compressed air, say at 10 to 20 p.s.i. or higher pressures.

As will be apparent from FIGURES 2 to 4, when the device 10 is inserted into a concrete mix and positioned inwardly adjacent a return surface, such as the upper mold surface 30, the fluid escaping from the openings 18 will be constrained into the flow paths 32 between the conduits 16 as indicated by the arrows in FIGURE 3. Desirably the frame 12 of the device is also provided with a plurality of perforations or openings 34 to facilitate movement of the paddle-like portion of the device through the stiff concrete. The openings 34 also provide transverse flow paths allowing some water or air to escape into the area behind the paddle, so that the zone of action of the upwardly rising stream of fluid issuing from the conduits 16 is substantially enlarged.

In carrying out the method of the invention, concrete is poured into a suitable mold, such as the octagonal piling form 40, and allowed to remain in a quiescent state until For most concrete mixes, a curing period of about 10 to 20 minutes (usually about 15 minutes) will suflice. The device It can be employed to initially agitate and knead the mix adjacent the return surfaces 30 of the mold, with the interrupted openings 34 permitting a certain freedom of movement of the paddle through the mix. In a preferred procedure, the paddle portion 12 of the device is first positioned well inwardly of the return surface 35*, as illustrated in FIGURE 5A. It will be noted that in this position the stream of fluid rising from the openings 18 tends to channel through the mix and carry with it the pockets 42 of entrapped water and air. The device is now slowly rotated into an outermost position in which the upper surfaces of the conduits 16- engage the inner or return surface 30 of the mold. In this position the fluid stream is forced upwardly with considerable pressure, increasing the upward channeling action of the entrapped air and water pockets. The device 10 can now be gradually removed, as illustrated in FIGURES 5B and C, so as to insure a desired complete elimination of the water pockets 42. Thereafter the upper exposed surface of the mix, at 46, can be worked and smoothed by hand to provide an unmarked exterior surface.

From the above description of an exemplary procedure and embodiment, it will be apparent that the present invention makes possible a simplified means of treating concrete mixes during their curing to form precast or molded objects that are virtually free of exterior deformations caused by entrapped water or air. Moreover, the procedures of the present invention are readily adaptable to existing manufacturing operations, as the equipment required is inexpensive and makes use of readily available sources of supply.

Various embodiments and differing applications of the 1y along the length of the conduits. Likewise the width of the frame 12 may be much greater than its length, in contrast to the particular structure disclosed. Accordingly it should be understood that the disclosures and description herein are purely illustrative and are not intended to be in any sense limiting.

I dlaim:

1. A method of forming a molded concrete structure with a prepared upper return surface comprising the steps of pouring concrete into a mold having an upper return surface, allowing the poured concrete to remain in a quiescent state until partially set, slowly kneading a subsurface volume of the concrete adjacent said return surface while passing an upwardly rising stream of fluid through said volume, said kneading step including a straining of said volume commencing inwardly of said surface and proceeding slowly to said surface.

2. The invention according to claim 1 passing a plurality of upwardly rising independent fluid streams through said volume.

3. A method as in claim 1 wherein said upwardly rising stream of fluid originates adjacent lower portions of such return surfaces.

4 4. A method as in claim 1 wherein said concrete is allowed to set prior to the action of said stream of fluid for a period of from ten to twenty minutes.

5. A method as in claim 1 wherein said fluid is air. 6. A method as in claim 1 wherein said fluid is Water.

References Cited in the file of this patent UNITED STATES PATENTS 823,457 Wilson June 12, 1906 1,911,966 Pickop May 30, 1933 1,961,388 Pickup June 5, 1934 2,055,514 Whiting Sept. 29, 1936 2,411,317 Day Nov. 19, 1946 2,476,551 Johnson July 19, 1949 2,528,643 Dubbs Nov. 7, 1950 2,638,655 Creskofif May 19, 1953 2,674,775 Wil'lson Apr. 13, 1954 2,841,856 Gelbman July 8, 1958 FOREIGN PATENTS 52,667 Netherlands June 15, 1942 

